EXCRETORY SYSTEM:

The job of the excretory system is to remove various produced by the body. The removal is known as excreation. It is important for the body to remove these various waste, also known as toxic, because toxic build up can lead to servere death.

About sixty percent of our body contains water. A portion of the water is in the tissues and cells. The water contains salt. the salt needs to be kept at the right concentrations. If there is little salt the body feeds it more, if there is too much salt the body gets rid of the salt not needed. This is the task of the two Kidneys.

The liver acts as a filter for the blood. It cleans out toxic waste and acid in the blood.

The skin plays a major role in excreation. It helps the body get rid of excess water, salts, and waste such as urea.

KIDNEYS:
Sixty percent of the human body wight is water, over half of which is inside the body cells and tissues. The rest of the water bathes all the body's cells. This water contains salt. The amount of salt in the watery blood tissue, is very important. Too much or too little salt can lead to servere problems, therefore, the salt in the body's water has to be kept at exactly the same concentrations. That task is the job of the Kidneys.

Each bean shaped kidney is divided into inner and an outer section. The outer section contains millions of chemical filtering factors called nephrons.

Blood is carried by the arteries into the inner section of the kidneys. When the blood gets into the kidneys, the blood travels into smaller and smaller arteries. Eventually, it enters a cluster of capillaries. Various substance in the blood, including water, salts, digested food particles, and other materials are filtered out of the blood here. A nitrogen waste, known as urea, is also filtered out of the blood. Then these substances pass into a cup-shaped part of the nephron called the capsule. The capsule leads to a set of tiny tubes in the nephron.

As the filtered material moves through pipe like passages in the nephron, much of the water and digested food that was filtered out of the blood is reabsorbed into the blood stream. This liquid that is left after reabsorption is called urine.

In the inner section of the kidney the, the urine passes through a cone shaped area into a funnel shaped area. This area is connected to a tube called the ureter, which conducts the urine to the urinary bladder. The urinary bladder is a sac of tissue that has the ability to expand as it fills with urine. Eventually, the urine passes out of the body through a tube at the bottom of the bladder called the urethra.

--CIRCULATORY SYSTEM:

A typical person has around 4-5 litres of blood. The blood is the transport system by which oxygen and nutrients reach the body's cells, and waste materials are carried away. In addition, blood carries substances called hormones, which control body processes, and antibodies to fight invading germs. The heart, a muscular organ, positioned behind the ribcage and between the lungs, is the pump that keeps this transport system moving.
Our heart is about the size of our clenched fist. It has thick muscular walls and is divided into two pumps. Each pump has two chambers. The upper, smaller, thin-walled atrium receives blood coming in from the veins. The blood flows through a one-way valve, which makes sure it always moves in the correct direction, into the larger, lower chamber called the ventricle. It has thick strong walls that contract to squeeze blood through another valve, out into the arteries.

Two-part Circulation

The body's circulation has two parts, with the heart acting as a double pump. Blood from the right side pump is dark red (bluish) and low in oxygen. It travels along pulmonary arteries to the lungs where it receives fresh supplies of oxygen and becomes bright red. It flows along pulmonary veins back to the heart's left side pump.

Blood leaves the left side of the heart and travels through arteries which gradually divide into capillaries. In the capillaries, food and oxygen are released to the body cells, and carbon dioxide and other waste products are returned to the bloodstream.The blood then travels in veins back to the right side of the heart, and the whole process begins again.

--NERVOUS SYSTEM:

Communication is vital to the survival of living organisms.To interact with their environment, multicellular organisms have developed a communication system at the Cellular Level..Specialized Cells (Neurons) allow Messages to be carried from one cell to another so that communication among all body parts is smooth and efficient. In HUMANS, these Cells called NEURONS make up the Nervous System.
The Nervous System CONTROLS and COORDINATES ALL ESSENTIAL FUNCTIONS of the Human Body. The Nervous System RECEIVES and RELAYS information about activities within the body and Monitors and Responds to INTERNAL and EXTERNAL CHANGES.
The Nervous System has FOUR FUNCTIONS that enable the body to respond quickly. The Nervous System:

A. Gathers information both from the outside world and from inside the body. SENSORY FUNCTION

B. Transmits the information to the processing area of the brain and spinal cord.

C. Processes the information to determine the best response. INTEGRATIVE FUNCTION

D. Sends information to muscles, glands, and organs (effectors) so they can respond correctly. Muscular contraction or glandular secretions. MOTOR FUNCTION The Nervous System has TWO Major Divisions.

A. The Central Nervous System (CNS) consist of the Brain and the Spinal Cord. The Spinal Cord carries messages from the body to the Brain, where they are analyzed and interpreted. Response Messages are then passed from the Brain through the Spinal Cord and to the rest of the Body.

B. The Peripheral Nervous System (PNS) consists of the neurons NOT Included in the Brain and Spinal Cord. Some Peripheral Neurons Collect Information from the Body and Transmit it TOWARD the CNS. These are called AFFERENT NEURONS. Other Peripheral Neurons Transmit Information AWAY from the CNS. These are called EFFERENT NEURONS.

The Functioning Nervous System is an enormous network of "one-way streets".

THE NEURON

The CELLS that Carry Messages Throughout the Nervous System are called NEURONS.
The Neuron is the Basic Functional Unit of the Nervous System.
Whatever their specific function, all neurons have the same physical parts: The Cell Body, Dendrites and One Axon.
Messages take the form of ELECTRICAL SIGNALS, and are known as IMPULSES. A Neuron carries impulses in only ONE direction.

Neurons can be classified into THREE TYPES:

A. SENSORY (RECEPTOR) NEURONS (AFFERENT) - Carry impulses from the SENSE ORGANS (RECEPTORS) to the Brain and Spinal Cord. Receptors detect external or internal changes and send the information to the Central Nervous System in the form of impulses by way of the Afferent Neurons.

B. MOTOR NEURONS (EFFERENT) - Carry impulses from the Brain and Spinal Cord to MUSCLES or GLANDS. Muscles and Glands are Two Types of Effectors. In response to impulses, Muscles Contract and Glands Secrete.

C. INTERNEURONS - Connect Sensory and Motor neurons and carry impulses between them. They are found entirely within the Central Nervous System.


--KIDNEYS:

The structure of the Kidney is as follows:

RENAL VEIN:

This has a large diameter and a thin wall. It carries blood away from the kidney and back to the right hand side of the heart. Blood in the kidney has had all its urea removed. Urea is produced by your liver to get rid of excess amino-acids.

Blood in the renal vein also has exactly the right amount of water and salts. This is because the kidney gets rid of excess water and salts. The kidney is controlled by the brain. A hormone in our blood called Anti-Diuretic Hormone (ADH for short) is used to control exactly how much water is excreted.


RENAL ARTERY:

This blood vessel supplies blood to the kidney from the left hand side of the heart. This blood must contain glucose and oxygen because the kidney has to work hard producing urine. Blood in the renal artery must have sufficient pressure or the kidney will not be able to filter the blood.

Blood supplied to the kidney contains a toxic product called urea which must be removed from the blood. It may have too much salt and too much water. The kidney removes these excess materials; that is its function.


PELVIS:
This is the region of the kidney where urine collects. If you are very unlucky, you may develop kidney stones. Sometimes the salts in the urine crystallise in the pelvis and form a solid mass which prevents urine from draining out of the medulla of the kidney.

MEDULLA:

The medulla is the inside part of the kidney. , it is a very dark red colour. This is where the amount of salt and water in urine is controlled.

CORTEX:

The cortex is the outer part of the kidney. This is where blood is filtered. We call this process "ultra-filtration" or "high pressure filtration" because it only works if the blood entering the kidney in the renal artery is at high pressure.

Billions of glomeruli are found in the cortex. A glomerulus is a tiny ball of capillaries. Each glomerulus is surrounded by a "Bowman's Capsule". Glomeruli leak. Things like red blood cells, white blood cells, platelets and fibrinogen stay in the blood vessels. Most of the plasma leaks out into the Bowman's capsules. This is about 160 litres of liquid every 24 hours.

Most of this liquid, which we call "ultra-filtrate" is re-absorbed in the medulla and put back into the blood.